The present invention relates generally to a thread cutting device for lock stitch sewing machines which are pneumatically controlled.
The desirability of providing a sewing machine having an integral thread cutting mechanism associated therewith has been long recognized in the art. In this manner, an operator can advance from one work piece to a successive work piece in a minimal amount of time without having to perform operations not truly directed to high production techniques. To this end, attempts have been made to provide thread cutting mechanisms which are reliable in use and not only provide the residual needle and bobbin threads from the preceding work piece to be at a minimal length, but also allow the sewing machine to be oriented and adapted to engage a successive work piece without having to adjust or rethread the machine in any manner.
The following patents reflect the state of the art of which applicant is aware, in so far as these references appear germane to the patent process:
U.S. Pat. Nos. 1,450,531 Weis; PA1 1,878,480 Fifield; PA1 3,051,111 Cortese et al.; PA1 3,403,648 Jarrett; PA1 3,418,953 Fowler; PA1 3,859,940 Nakamura; PA1 4,200,050 Bianchi.
Of these references, the Cortese et al. patent is directed to a sewing machine thread cutter wherein cutting of the sewing thread is obtained by a breaking action utilizing a device actuated by a predetermined overthrow designed into the stop motion mechanism which stops the sewing machine when the sewing cycle is completed.
The Bianchi patent relates to a thread cutting device for a sewing machine which includes a catcher member having a notched plate for catching the needle thread together with a small foil providing a bobbin thread catching zone and a bobbin and needle cutting zone.
The Nakamura patent relates to a thread cutting device for a sewing machine wherein a thread cutting cam is arranged for rotation with the main shaft together with a reciprocal shifter and a thread cutting mechanism for shearing a thread in accordance with a reciprocal movement of the shifter.
The Weiss patent relates to a thread breaking mechanism wherein the pull of the feed rolls for the fabric breaks the needle thread loop across the under edge of a looper blade and the bottom thread is broken across a breaker plate upon completion of the backward movement of the breaker slide.
The Fifield patent relates to a thread cutting mechanism for sewing machines for severing both the needle and bobbin threads on the machine. In the Fifield structure, a cutter blade 52 passes over a stationary blade 54 in a bobbin thread pull-off and severing device connected to the work-clamp opening mechanism together with needle-loop detaining and severing means including a pair of superposed pointed blades 63, 64.
The Fowler patent is directed to an automatic thread cutting attachment for an industrial sewing machine which is driven by a feed dog activating bar. A bracket attached to the feed dog activating bar supports a pivotal lever which is reciprocated at one end and which at the other end actuates the movable blade of the thread cutter.
The Jarrett patent discloses an attachment for a sewing machine which includes a device for pulling a loop in the thread adjacent the bobbin which is tensioned for severing substantially simultaneously with the severing of the tail. Jarrett provides an air cylinder 38 for pivotally reciprocating a knife 35. A thread looping device is also provided having a thread hook 32 which sweeps past the needle aperature 31 for engagement with the thread extending down from the needle to the bobbin so as to pull a loop in the thread. The sewing action of the needle, clamping action of the arch clamp, the cutting action of the knife in a horizontal plane and the looping function of the thread hooks are all coordinated so that they operate in proper sequence for bar tacking and severing.
By way of contrast, the instant application is directed to and specifies a pneumatic thread undercutting device for use in conjunction with a pneumatic type of needle positioner similar to the one disclosed in my pending application U.S. Ser. No. 244,589 entitled NEEDLE POSITIONER FOR SEWING MACHINE, which has advantages and benefits not contemplated by the prior art, while simultaneously overcoming disadvantages inherent therewithin. The undercutter includes a frame disposed beneath a sewing area surface, pneumatic means carried on the frame having an extensible rod and a moving blade operatively connected to the extensible rod so as to reciprocally and laterally translate in a linear fashion; a stationary blade associated with the moving blade in such a manner that of the two threads is initially severed by the moving blade, the second thread being severed by the stationary blade and appropriate structure for the bobbin and moving and stationary blades are provided so as to assure predetermined lengths of the needle and bobbin threads so that not only will the initial work piece not have an objectionable threaded terminus requiring subsequent snipping, but the successive work piece will be able to enter the machine without any further adjustments by the operator. In this manner, the volume of work can be increased on the machine.
Equally important, the vertical dispostion of the apparatus of the instant application removes the device so that should a needle break and fall below the sewing surface, the broken needle part will not become entrained in the cutting mechanism, thereby obviating any mechanical damage or inordinate repairs, and providing a more reliable, easily repairable machine.